Cardiovascular disease (CVD) is the number one cause of mortality in the United States. The most common form of CVD is atherosclerosis which characterized by chronic inflammation resulting in the formation of plaques in the arteries. Inflammation is initiated by the sequestration of low-density lipoproteins (LDL) in the vessel wall where they become oxidized (ox-LDL) and cause damage to local cells. This results in the recruitment of antigen presenting cells (APCs) including dendritic cells (DCs). While oxLDL antibody titers and resulting immune complexes (oxLDL-ICs) correlate with disease severity, it is unknown if oxLDL-ICs play a role in disease pathogenesis. Studies in macrophage cell lines have shown increased cellular activation following oxLDL-IC treatment. However, the role of DCs in this process is largely unstudied, and reports regarding the in vivo relevance are lacking. Preliminary data from our lab show that oxLDL-ICs cause increased DC activation as measured by expression of activation markers and secretion of pro-inflammatory cytokines. These in vitro studies suggest an atherogenic role for oxLDL-ICs. Given the potent ability of DCs to elicit a downstream immune response, understanding oxLDL-IC mediated DC activation will fill a critical gap in our knowledge of CVD pathogenesis and provide new avenues for therapeutic intervention. We propose two aims to determine the effects of oxLDL-ICs on DCs and the implication of these effects on atherosclerotic outcomes.
In aim 1, we will determine the mechanism by which oxLDL-ICs modulate DC activation and cytokine production. It is likely that oxLDL-ICs activate DCs through binding and internalization by Fc? receptors (Fc?Rs), which recognize the Fc portion of ICs and can be found on several leukocyte populations including DCs. However, given that oxLDL is known to bind other cell surface receptors including TLR4 and CD36, we believe that oxLDL-ICs may increase inflammation by concomitant interaction with several cell surface receptors. We will test this hypothesis by treating bone marrow derived DCs from wild type (C57BL/6) mice and receptor- specific knock-out mice with oxLDL or oxLDL-ICs. Activation will be measured by flow cytometry and cytokine production. BMDC will also be co-cultured with T cells to determine their ability to elicit an immune response.
In aim 2, we will determine the effects of dendritic cell specific Fc?R on atherosclerosis. Given the robust capacity of DCs to activate and differentiate nave T cells and thus control downstream immune responses, DC Fc?Rs are likely to be important in mediating atherosclerotic outcomes. To identify how DC Fc?R mediate atherosclerosis, we will perform an adoptive transfer of wild type or Fc?R-/- DC into LDLr-/- mice. Additionally, we will perform a bone marrow transplant of the progeny from Fc?Rflox/flox mice crossed with CD11c Cre+ mice to obtain DC specific Fc?R knockouts into LDLr-/- mice. Collectively, the proposed studies will identify a role for oxLDL-ICs in atherosclerosis.
Atherosclerosis begins with the accumulation of LDL or 'bad' cholesterol in the blood vessels where it becomes modified ultimately resulting in the generation of an immune response and accumulation of plaque in the arteries. Part of this immune response is generation of antibodies to modified LDL, but it is currently unclear whether these antibodies protect against atherosclerosis or exacerbate the disease. Our proposal seeks to define a role for antibodies to modified LDL in atherosclerosis.
| Rhoads, Jillian P; Lukens, John R; Wilhelm, Ashley J et al. (2017) Oxidized Low-Density Lipoprotein Immune Complex Priming of the Nlrp3 Inflammasome Involves TLR and Fc?R Cooperation and Is Dependent on CARD9. J Immunol 198:2105-2114 |
